1. Field of the Invention
The present invention relates generally to a heat insulating shield for an automotive vehicle. More particularly, the present relates to a heat shield for an automotive vehicle, the shield including a phase change material for heat absorption.
2. Disclosure Information
It is known in the automotive industry that various components within the vehicle generate large amounts of heat which must be shielded from other components in the vehicle. For example, the exhaust system of a vehicle typically is located beneath the underbody or floorpan of the vehicle and generates a large amount of heat during operation of the vehicle. It is desirable to prevent the transfer of the heat generated from the exhaust system to the interior of the vehicle through the floorpan. Typically, this is done through a large, heavy, stamped metal shield interposed between the vehicle floorpan and the exhaust system components. In certain vehicle operating conditions, the exhaust system, as well as other components, produce heat in very different amounts over different lengths of time. For example, when a vehicle is pulling a trailer up a steep hill, the vehicle engine uses a lot of energy and produces excess heat which is passed through the exhaust system. As long as the vehicle continues to move, the heat is shed from the vehicle by the air movement caused by the moving vehicle and does not cause any significant heating problem. If the vehicle slows or comes to a stop at the crest of the hill, all of the heat bellows from the exhaust system onto the shielding until the exhaust system sufficiently cools. Because of these kinds of scenarios, shields have been overdesigned becoming larger and heavier to account for such operating conditions. A large shield must be used to fully encompass the component to be protected and deflect the large amount of heat generated in such a specific operating condition. By making the shields larger and heavier, there are cost and weight penalties associated with that component on the vehicle.
It would, therefore, be desirable to provide a smaller heat shield to be used in an automotive vehicle which absorbs all of the excess heat generated by a heat source or heat generating component and which avoids the disadvantages of the known heat shield systems.
The general principles of thermal energy storage by means of phase change materials are widely known. As materials are heated from a beginning state or phase, the solid phase, for example, to the liquid phase, energy is absorbed. In the temperature range at which the material changes from one phase to another, more energy is required to raise a temperature to an additional increment than to raise the temperature by the same increment when the material is not changing phase. This additional energy required at the phase change (or transition from one state to another) of the material is called the latent heat of transition. The singular advantage of phase change materials is their ability to absorb large amounts of heat during the melting period without increasing substantially in temperature.
Phase change materials have been used in the automotive arts before. For example, U.S. Pat. No. 4,258,677 discloses an elongated canister having a phase change material therein which surrounds an exhaust system. A heat exchanger is located in the top of the canister and the canister is filled with a phase change material. When the exhaust system is warmed, the phase change material transfers the heat of the exhaust system to the heat exchanger which then transfers the heat to a separate component within the engine to provide for additional heat in the engine. However, the patent does not teach the use of a phase change material as a heat shield for specific components within the vehicle as suggested by the present invention.
Numerous other systems have been proposed which utilize a phase change material for storing heat such as disclosed in U.S. Pat. Nos. 4,817,704 and 5,007,478. However, none of the systems teach or suggest the use of such a phase change material to provide thermal energy insulation to an automotive vehicle component. The present invention provides, however, a new, lightweight heat shield for an automotive vehicle which overcomes the problems associated with known heat shield structures at a reduced size penalty.